In a wireless communication system such as PHS (Personal Handy phone System) performing wireless communication within a communication area by dividing the communication area into a plurality of micro cells and providing a base station for each of the micro cells, so-called handover which changes a base station as a communication object due to movement between the micro cells frequently occurs, so that there has been difficulty in maintaining communication quality. In addition, during high speed movement in subway, especially, in a bullet train or an automobile, handover between micro cell base stations cannot be performed timely, and thereby causing call disconnections.
The frequency of handovers can be reduced by simply broadening communication coverage of micro cells to be macro cells. However, since advantages of micro cells are lost, it is concerned that wireless capacity would be reduced in an area where traffic to a base station is high.
Thus, a technique of providing a communication area where a micro cell and a macro cell are overlapped and selecting a cell in accordance with a current communication condition has been disclosed (for example, JP-A-2004-535143). In addition, a technique of calculating a speed of a mobile station based on a stay time period in a micro cell (for example, JP-A-H9-139974) or by using a speed sensor and performing changeover between a micro cell and a macro cell in accordance with the speed has been disclosed.